Electric vehicles and plug-in hybrid vehicles have inverter devices that allow electric motors to be driven by high voltage batteries for power drive, and low voltage batteries for activating accessories of the vehicles such as lights and radios. In this type of vehicle, a DC-to-DC converter device is mounted that converts electrical power for the high voltage battery to that for the low voltage battery or converts electrical power for the low voltage battery to that for the high voltage battery. The C-to-DC converter device includes a high-voltage side switching circuit that converts high-voltage direct current to alternating current, a transformer that converts alternating current high voltage to alternating current low voltage, a low-voltage side switching circuit that converts low alternating voltage to direct current, a filter circuit that reduces noise conduction to the outside of the DC-to-DC converter device, and a control circuit board that generates control signals for controlling the switching circuits, and other components.
In this type of DC-to-DC converter devices, electromagnetic noise (radiation noise) that leaks from the switching circuits and the transformer propagates to the filter circuit and the control circuit board, so that the noise leaks to the outside of the electrical power converting device via harnesses and the like. This electromagnetic noise becomes a problem. A structure having a shielding part for noise shielding provided between noise sources (transformers and switching circuits) and a filter circuit has been proposed as a method of suppressing such a noise propagation (e.g., see PTL1).